Abstract
The heartbeat has been proposed as an intrinsic source of motion that can be used in combination with tagged Magnetic Resonance Imaging (MRI) to measure displacements induced in the liver as an index of liver stiffness. Optimizing a tagged MRI acquisition protocol in terms of sensitivity to these displacements, which are in the order of pixel size, is necessary to develop the method as a quantification tool for staging fibrosis. We reproduced a study of cardiac-induced strain in the liver at 3T and simulated tagged MR images with different grid tag patterns to evaluate the performance of the Harmonic Phase (HARP) image analysis method and its dependence on the parameters of tag spacing and grid angle. The Partial Volume Effect (PVE), T1 relaxation, and different levels of noise were taken into account. Four displacement fields of increasing intensity were created and applied to the tagged MR images of the liver. These fields simulated the deformation at different liver stiffnesses. An Error Index (EI) was calculated to evaluate the estimation accuracy for various parameter values. In the absence of noise, the estimation accuracy of the displacement fields increased as tag spacings decreased. EIs for each of the four displacement fields were lower at 0° and the local minima of the EI were found to correspond to multiples of pixel size. The accuracy of the estimation decreased for increasing levels of added noise; as the level increased, the improved estimation caused by decreasing the tag spacing tended to zero. The optimal tag spacing turned out to be a compromise between the smallest tag period that is a multiple of the pixel size and is achievable in a real acquisition and the tag spacing that guarantees an accurate liver displacement measure in the presence of realistic levels of noise.
Highlights
The increasing interest in the development of a non-invasive tool to assess liver fibrosis had led to several studies on Magnetic Resonance Elastography (MRE) [1,2]
To measure the deformations, which are supposed to be related to liver stiffness and could be used as an index of fibrosis, investigators have proposed a method based on the use of tagged Magnetic Resonance Imaging (MRI)
It is very important to define an acquisition protocol that identifies the optimal angle and tag spacing of the grid applied to the images to maximize the sensitivity to these small liver displacements
Summary
The increasing interest in the development of a non-invasive tool to assess liver fibrosis had led to several studies on Magnetic Resonance Elastography (MRE) [1,2]. MRE has shown a high correlation between liver mechanical properties and fibrosis stages [3,4,5,6,7], but it requires a special-purpose external vibration source as well as dedicated acquisition sequences. It allows the evaluation of the right hepatic lobe only. To measure the deformations, which are supposed to be related to liver stiffness and could be used as an index of fibrosis, investigators have proposed a method based on the use of tagged Magnetic Resonance Imaging (MRI). It is very important to define an acquisition protocol that identifies the optimal angle and tag spacing of the grid applied to the images to maximize the sensitivity to these small liver displacements (that are in the order of a typical pixel size)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
